The ECU crosses from the lateral to the medial side of the forearm. The EDM takes a similar course as the EI except it follows the ED tendon along the little finger. On the back of the hand, the ED tendons diverge to follow the fingers and the EI tendon joins the ulnar side of one of the ED tendons along the back of the index finger. The ED divides into four tendons which, with the EI tendons, go through the fourth tendon compartment of the dorsal carpal ligament. They then pass beneath the extensor retinaculum and dorsal carpal ligament, where they lie in a groove on the back of the radius, immediately behind the styloid process, and continue into the second tendon compartment. Their muscle fibers end at the upper third and the mid forearm respectively, continuing as flat tendons along the lateral border of the radius, beneath the APL and EPB. The ECRL and ECRB, (with the brachioradialis) form the lateral compartment. The APL, EPB, EPL, and EI all have an additional origin at the interosseus membrane. The EPL arises from the dorsal surface of the ulna and the EI from the distal third of the dorsal part of the body of ulna. The EPB arises from the radius distal to the APL and from the dorsal surface of the radius. The APL originates from the lateral part of the dorsal surface of the body of the ulna below the insertion of the anconeus and from the middle third of the dorsal surface of the body of the radius. Moving distally, there are the abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis (EI). The ECRB has additional origins from the radial collateral ligament, the ECU from the dorsal border of the ulna (shared with the flexor carpi ulnaris and flexor digitorum profundus), and all four also originate from various fascia.
Distal to this, the extensor carpi radialis brevis (ECRB), extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris (ECU) originate from the lateral epicondyle via the common extensor tendon. It originates just distal to the brachioradialis at the lateral supracondylar ridge of the humerus, the lateral intermuscular septum, and by a few fibers at the lateral epicondyle of the humerus. The extensor carpi radialis longus (ECRL) has the most proximal origin of the extrinsic hand extensors.